The point of training a dog to bark on command, is that it becomes a way to stress the dog, and then he resolves the stress by a clean, clear, deep bark. Why is this important? Because it gives the dog a way to express fear without having to act on fear. In this sequence we see the sable GSD bark at the Westy rather than having to grab him with his jaws (the more primal expression of physical grounding) and this has the effect of keeping the Westy calm. The Westy can feel that the GSD is moving its energy rather than trying to hold it in, and energy that moves is safe, energy that is being held back is always dangerous.